An object is to provide a steel material for line pipes having a heavy wall thickness of 30 mm or more, a high strength, excellent low-temperature toughness, and an excellent DWTT property in order to address the application of the steel material for line pipes to offshore pipelines, a method for producing the steel material for line pipes, and a method for producing a line pipe.
A method for producing a steel material for line pipes which has a tensile strength of 570 MPa or more, a compressive strength of 440 MPa or more, and a thickness of 30 mm or more, the method including heating a steel having a specific composition to a temperature of 1000°C to 1200°C; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature + 20°C) or less is 50% or more, and a rolling finish temperature is the Ar 3 transformation point or more and 790°C or less, the rolling finish temperature being an average temperature of a steel plate; subsequently performing accelerated cooling from a temperature of the Ar 3 transformation point or more, at a cooling rate of 10 °C/s or more, to a cooling stop temperature of 200°C to 450°C, the cooling stop temperature being an average temperature of the steel plate; and then performing reheating such that the temperature of a surface of the steel plate is 350°C to 550°C and the temperature of the center of the steel plate is less than 550°C.